1. Field of the Invention
The invention is related to the production method of group III-nitride wafers using ammonothermal method and subsequent testing method and the group III-nitride wafers with test certificate data.
2. Description of the Existing Technology
(Note: This patent application refers several publications and patents as indicated with numbers within brackets, e.g., [x]. A list of these publications and patents can be found in the section entitled “References.”)
Gallium nitride (GaN) and its related group III alloys are important materials for various opto-electronic and electronic devices such as light emitting diodes (LEDs), laser diodes (LDs), microwave power transistors, and solar-blind photo detectors. Currently LEDs are widely used in cell phones, indicators, displays, and LDs are used in data storage discs. However, the majority of these devices are grown epitaxially on heterogeneous substrates, such as sapphire and silicon carbide since GaN wafers are extremely expensive compared to these heteroepitaxial substrates. The heteroepitaxial growth of group III-nitride causes highly defected or even cracked films, which hinders the realization of high-end optical and electronic devices, such as high-brightness LEDs for general lighting or high-power microwave transistors.
To solve problems caused by heteroepitaxy, it is helpful to utilize single crystalline group III-nitride wafers sliced from bulk group III-nitride crystal ingots. For a majority of devices, single crystalline GaN wafers are favored because it is relatively easy to control the conductivity of the wafer, and a GaN wafer will provide small lattice/thermal mismatch with device layers. However, due to the high melting point and high nitrogen vapor pressure at high temperature, it has been difficult to grow group III-nitride crystal ingots. Growth methods using molten Ga, such as high-pressure high-temperature synthesis [1,2] and sodium flux [3,4], have been proposed to grow GaN crystals. However, the crystal shape grown in molten Ga becomes a thin platelet because molten Ga has low solubility of nitrogen and a low diffusion coefficient of nitrogen.
Currently, only hydride vapor phase epitaxy (HVPE) can produce commercial GaN wafers. In HVPE, a thick (0.5-3 mm) GaN film is grown on a heteroexpitaxial substrate such as sapphire or gallium arsenide. The substrate is subsequently removed and a free-standing GaN wafer is finished by grinding and polishing. Since the GaN wafer is produced one by one on each heterogeneous substrate, each produced GaN wafer is tested before shipping. However, as the production volume increases, it becomes extremely time consuming to test all wafers before shipping.